Remember that

So if
and
, then we know
.
Then use the Pythagorean identity to solve for cosine:

Answer:37$ for the shirt Sales tax: $2.04
Cost/Price before ST: $37.00
Total Cost/Price including ST: $39.04
for the belt
Sales tax: $0.68
■ Cost/Price before ST: $12.36
■ Total Cost/Price including ST: $13.04
Step-by-step explanation:
The one that is wrong is. C. If all the x’s are different it is a function